1. Field of the Invention
The invention relates to hydroxyalkyl-functionalized fillers, to a process for preparing them, and to their use.
2. Description of the Related Art
A filler is a finely divided solid which alters the properties of a matrix to which it is added. Fillers are presently in use in the chemical industry for numerous purposes. They may alter the mechanical properties of plastics, such as hardness, tensile strength, chemical resistance, electrical or thermal conductivities, adhesion or else the contraction experienced in the event of temperature changes. Further factors they influence include the rheological behavior of polymeric melts. Functionalizing fillers with chemically reactive groups can improve their compatibility with the matrix and hence also optimize the profile of properties of the formulated compound. Preferred groups in this context are those able to react with the matrix itself, such as carbinol groups, which are able to react with polyesters, polyurethanes or polyacrylates, for example. In formulations, appropriate modification of the fillers and/or particle surface ensures compatibility of the particle with the surrounding polymer matrix. Moreover, where the particle surface possesses appropriate reactivity toward the matrix, such that under the particular curing conditions of the formulation it is able to react with the binder system, the particles can be incorporated chemically into the matrix in the course of curing, such incorporation frequently having a positive effect on the profile of properties of the formulated compound.
EP 768347 describes a method of treating fillers that starts from specific cyclic silanes of the general formula I which can be consumed by reaction with metal hydroxide functions to form carbinol groups.

In this formula R1 is a carbon radical having up to 20 carbon atoms, R2 is hydrogen or a hydrocarbon radical having up to 20 carbon atoms, and a commonly has a value of 3 or 4. Particular attention is drawn to the fact that the reaction is performed without the use of catalysts at temperatures between 25° C. and 150° C. In practice, however, a number of problems arise during the implementation of the method: although it is possible to obtain a stable six-membered ring with a=4, doing so nevertheless requires an elevated reaction temperature and significantly prolonged reaction times in the reaction with metal hydroxide functions or silanol end groups. The synthesis of this stable 6-membered ring, moreover, requires a very complicated process, in which an organometallic silicon compound is inserted into a tetrahydrofuran ring. The 5-membered rings that are reactive in the sense of EP 768347 are unstable substances which tend toward decomposition or autopolymerization. Consequently the method described in EP 768347 is poorly suited to industrial use, since the silane compounds used either cannot be stably obtained or are accessible only by way of technically complex synthesis techniques.